Probably the Hags, they've always seemed off putting to me, someone really creep and sickening about them. Though thats more from the film then the book. But since the saw the film first that's how I imagine them.

“I'm on Aslan's side even if there isn't any Aslan to lead it. I'm going to live as like a Narnian as I can even if there isn't any Narnia.”

I can't decide between them, but maybe the boggles, spectres, ghouls, werewolves and minotaurs are scariest - somehow they have the ability to scare badly, either by supernatural aspect or by physical force. The ogres and giants somehow don't feel quite so bad, but they probably are.

“Stale water is a poor drink,' said Annlaw. 'Stale skill is worse. And the man who walks in his own footsteps only ends where he began.”― Lloyd Alexander, Taran Wanderer

Fair point, Movie Aristotle, so I ticked that box. Of the other three I had ticked, they were the cruels, because of the obvious cruel intent, the ghouls because of the association with man's selfish inhumanity to man, and the boggles which boggles my mind.

With my username how could I possibly tick a werewolf? Frankly, that is a most hackneyed concept which would probably howl to the full moon shining on the White Witch's monster union if it was left out of the usual lineup. Especially after Sabine Baring-Gould wrote a whole book about werewolves and other sorts of ghostly dogs. J.K. Rowling decided that lycanthropy, that is to say, the condition of being one, was a disease inflicted on werewolves which caused them considerable pain. And I'd rather eat lettuce and get entangled in a tea strainer, in a Wagga Wagga telephone box, than read any of the Twilight series. I rather think that C.S.Lewis only included werewolves because wolves are real wild creatures, related though they are distantly to the ordinary domestic dog, some breeds of which are just as fearsome as wolves when owners use them for attack and intimidation.

As for hags, unfortunately, long before we reach old womanhood, it is all too often that one gets insulted by the term by rude, inconsiderate misogynists, which is probably intended to drive the victim into enough of a rage to want to earn the pejorative epithet by screeching like a banshee, which probably isn't even in the list.